Acupuncture has been used widely to treat disease; however, the time course for acupuncture to have an effect remains unclear. Therefore, the aim of the present study was to investigate the time course of changes in nail fold microcirculation (NFM) induced by acupuncture stimulation (AS) at the right and left Waiguan acupoints (WAs). A total of 38 healthy female volunteers, age range from 21 to 33, were studied. We recorded NFM of the right middle finger before, and 5 min, 10 min, 15 min and 20 min after initiating AS; NFM was also recorded 5 min and 10 min after secessions of AS. Nitric oxide (NO) and endothelin-1 levels were measured from the left cubital vein, before AS and 10 min after stopping AS. The results indicated that capillary density of NFM increased 5 min after AS at the right Waiguan acupoint (WA); however, similar changes were not noted at the left WA. The capillary density decreased beginning 15 min after AS at the right and left WA. Capillary red blood cell velocity increased 5 min and 10 min after AS at the right and left WAs, but decreased 5 min and 10 min after stopping AS at the left WA. NO and endothein-1 levels were similar before AS and 10 min after stopping AS. Therefore, we suggest that a segmental effect of the spinal nerve contributes to the increasing capillary density of NFM induced by AS. The effect of acupuncture on NFM lasts about 10-15 min. The changes of balance between the sympathetic nerve activities and parasympathetic nerve activities may be induced by AS.